Analysis on Optimal Configurations of Two-Hop Relay Network

Abstract

Fixed relay as a candidate solution in the cellular system attracts more and more attention due to its improvements of coverage and capacity. In this paper, we make our study on the optimal configurations of two-hop relay downlink system. Based on former works (2) (3) (4), two typical resource allocation schemes of the two hops are considered on the assumption of TDD system—one is in time domain and the other is in frequency domain. Based on the improved evaluation model, we demonstrate that it is critical to improve the capacity of the BS to RS link to achieve higher system throughput. Then, different RS positions are discussed in terms of the system throughput and the optimal deployment of Relay Station (RS) is concluded. In addition, we find that the ratio between the transmit power of base station (BS) and that of RS influences the throughput greatly. As is known, mobile communication has developed rapidly in recent years and at the same time the number of users of mobile communication users has increased at high speed. However, as the number of users and traffic increasing strongly, it has been found that the capacity of wireless communication networks has got enormous challenges. The limits of signal propagation, bandwidth, attenuation and noise make traditional communication technology improve hardly. To deal with all these limitations, several new technologies are proposed, among which relay technology attracts more and more attentions, since it is a new technology that is able to increase coverage for high data rates and capacity, while reducing deployment cost (1). As relay technology has so many advantages aforesaid mentioned to cope with shortcomings of conventional cellular networks, the evaluation of system performance is significant for the developing of 3G and B3G. Some work has been done as in (5-7). However, the system models proposed in those contributions can be improved. In (5), single cell BS and multi cell BS are studied, while the co-channel interference is not considered. In (6) (7), similar model is discussed. Four cells constitute a frequency reuse cluster in an FDD mode. The BS is located in the centre of the hexagonal cell. Six relay stations are placed in each cell, each of which is located on the line between the BS and the cell vertices. Such high frequency reuse factor will lead to the decrease of spectrum efficiency. Therefore, we have proposed a multi-cell system evaluation model with fixed relay station, which is more suitable for LTE system and far more reasonable than the models mentioned above. This paper will focus on the effect on the sector throughput by choosing different parameters and resource assignment schemes of relay system. We will demonstrate that to improve sector throughput it is critical to increase the average throughput of the BS to RS link. After that, we shall investigate the optimal position of RS and sector throughput under the two mainstream resource allocation schemes and evaluate which scheme is better. Then the ratio between the transmit power of BS and RS will be changed in order to show how these parameters affect sector throughput. The rest part of this paper is organized as follows. Section II gives a brief introduction of the architecture of the system model including cellular layout, antenna pattern and propagation model. Section III presents the evaluating method of sector throughput from the aspects of time domain and frequency domain resource allocation scheme separately. Corresponding simulation results are given and analyzed in Section IV. Finally, Section V contains the summaries and conclusions.